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   <TITLE> Zoltan Developer's Guide:  HIER</TITLE>
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<H2>
<A NAME="HIER"></A>Appendix: Hierarchical Partitioning (HIER)</H2>
&nbsp;

<H3>
Outline of Algorithm</H3>

<P>Zoltan's hierarchical balancing automates the creation of hierarchical
partitions.  The implementation of Hierarchical Partitioning (HIER) in Zoltan is
due to Jim Teresco (Williams College), with many suggestions and ideas
from the entire Zoltan team.<P>

The hierarchical balancing implementation utilizes a lightweight
intermediate structure and a set of callback functions that permit an
automated and efficient hierarchical balancing which can use any of
the procedures available within Zoltan without modification and in any
combination.  Hierachical balancing is invoked by an application the
same way as other Zoltan procedures.  Since Zoltan is data-structure
neutral, it operates on generic "objects" and interfaces with
applications through callback functions.<P>

A hierarchical balancing step begins by building an intermediate
structure using the application-supplied callbacks.  The initial
structure is computed using <B>Zoltan_Build_Graph</B> to build the
same structure that is used to support partitioning using the Parmetis
and Jostle libraries.  The hierarchical balancing procedure then
provides its own callback functions to allow existing Zoltan
procedures to be used to query and update the intermediate structure
at each level of a hierarchical balancing.  The structure is augmented
to keep track of objects and their needed information during the
procedure.  After all levels of the hierarchical balancing have been
completed, Zoltan's usual migration arrays are constructed and
returned to the application.  Thus, only lightweight objects are
migrated internally between levels, not the (larger and more costly)
application data.  More details about the fields of the intermediate
structure and how the are used can be found in the Zoltan distribution
in <I>hier/README</I>.<P>

<BR>&nbsp;

<H3>
Data Structure Definitions</H3>

<P>There is one major data structure in HIER, defined in
<i>hier/hier.h</i>.  The <I>struct HierPartParamsStruct</I> includes
all information needed by the hierarchical balancing procedures.  The
fields are documented in comments in the structure definition.

<BR>&nbsp;

<H3>
Parameters</H3>

<P>The parameters used by HIER and their default values are described in the
<a href="../ug_html/ug_alg_hier.html">HIER section</a> of the <B><A HREF="../ug_html/ug.html">Zoltan User's
Guide</A></B>.  These can be set by use of the <b>Zoltan_Hier_Set_Param</b> subroutine
in the file <i>hier/hier.c</i>.
 
<BR>&nbsp;

<H3>
Main Routine</H3>

<P>The main routine for HIER is <b>Zoltan_Hier</b> in the file <i>hier/hier.c</i>.

<BR>&nbsp;
<BR>&nbsp;
<BR>&nbsp;

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